The invention relates to a pinch ring for controlling the shape of the so-called "thread balloon" in a spinning or twisting machine especially for use with threads which consist at least partially of modified polyester or polyacrylonitrile whose thread guide member is substantially a single helical loop with a smooth inner surface and a pitch which provides axial clearance between opposite thread guiding portions in adjacent windings of the loop.
The term "modified polyester or polyacrylonitrile fibers" refers to fibers which are so modified during manufacture that their longitudinal and lateral strength has been diminished so that these fibers will fracture more easily after repeated flexure. This feature prevents the formation of knots or similar accumulations during the processing of woven or knitted materials. Such accumulations would form unsightly small knots at the surface of the finished goods.
The balloon pinch rings which have been in use up to the present time permit only relatively low traveler speeds when used with yarns consisting at least partially of modified polyester or polyacrylonitrile fibers. These speeds are well below the traveler speeds usable with fibers of other compositions and this fact substantially reduces the production rate. The commonly used balloon pinch rings have a planar or helical loop (German Gebrauchsmuster 1380773); in the latter case the overlapping regions of the balloon pinch ring are separated by only a relatively small vertical clearance of approximately 2-3 mm.
It is also known to guard or confine the thread balloon over its entire height or a substantial portion of its height by means of a spiral wire cage (DT Pat. No. 169170, U.S. Pat. No. 2,660,856). Cages of this kind have not found any use in practice.
In order to reduce the damage to the thread, a known balloon pinch ring (DT Offenlegungsschrift 2242755) provides parallel ribs on at least part of the interior surface which comes in contact with the thread. These parallel ribs are disposed obliquely with respect to the passage of the thread. Manufacture of such a balloon pinch ring is quite complicated because the track for the thread is not smooth, but ribbed.